This study identified specific assessment and diagnostic competencies seen as important for masters level special educators. In Phase 1, objectives were gathered from the assessment courses of 61 universities preparing special education teachers. In Phase 2, an initial list of 128 competency statements (71 knowledge statements and 57 skill statements) was developed and organized by the steps of the typical assessment process. In Phase 3, this list was validated by 105 members of the Council for Educational Diagnostic Services. Forty-five knowledge items were rated as very important, with the two highest ratings going to knowledge of basic terminology used in assessment and understanding of assessment guidelines contained in federal law. Forty skill items were rated as very important, with gathering background information and identifying learners' ability to meet the demands of assessment procedures rated the highest. Comparison with ratings for beginning teacher skills found significant differences for both knowledge and skill items. An attached position paper of the Council for Educational Diagnostic Services, based on the findings of this study, lists the eight most critical areas of knowledge and skills for master teachers of any exceptionality. (DB)